1. Field of the invention
This invention relates to inflatable cushions, particularly cushions for wheelchairs, and to control devices for such cushions and other cellular inflatable human body supports.
2. Description of the prior art
It is well-known that people such as the disabled who are confined to a bed or a wheelchair for long periods of time frequently suffer from sores, which result from areas near the surface of the skin being deprived of blood due to pressure exerted on those areas by the bodily support under the person's body weight. In the context of beds it is known, for example from GB-A-1595417, to provide a mattress, comprising an array of hollow flexible tubes which are sequentially inflated and deflated, so that ripples travel along the length of the mattress. Thus, while a person's body is continuously supported by the mattress the actual regions of the body in contact with the mattress which bear the body weight change with time. This prevents any one area of the body being continuously deprived of blood and thus discourages the formation of sores.
There have been a number of attempts at applying a similar principle to seats for chairs and in particular wheelchairs, but up to now none has been particularly successful. The present inventors believe that in the context of a chair a rippling effect, as in the known mattress, is not suitable, because the support area for the body is smaller and a chair support demands a much higher degree of stability, i.e. it is important for the person to be always supported in the chair substantially vertically, without a tendency to tip in any one direction as the supporting areas on the body surface change. There is therefore a need for a cushion for a chair, which cushion continuously supports a person's body in a substantially vertical condition, with the regions of the cushion in contact with the body and thus bearing the body weight changing sequentially with time. It is one object of this invention to meet this need.
Mattresses having groups of inflatable cells and control systems for them are well known and are described for example in U.S. Pat. No. 4193149 and U.S. Pat. No. 4711275. Because such mattresses are primarily for use by patients who are incapable of moving themselves or can move only with difficulty, their control systems are complex.
Someone in a chair, e.g. a wheelchair, however, may not require such an elaborate and fail-safe control system. Power requirement should be minimized, since mains supply is not available. It is another object of the present invention to provide an inflation and a control device which is simple yet effective and requires little power.